Properties Of ALD Grown MoO₃ Thin Films

Molybdenum oxide（MoO₃） is a multi-crystalline semiconductor with wide bandgap and low carrier concentration,which is not suitable for an electronic device.While exposed in H2 environment, the MoO₃ thin films will switch to α-MoO_3-x film.The α-MoO_3-x thin film can be used to prepare field effect transistor（FET）. Meanwhile the MoO₃ thin film can switch to MoSe2 when exposed in Se environment. Therefore, based on the above theory, the contents of this thesis are as follows:（1） The thin films of MoO₃ has been obtained by the plasma enhancement atomic layer deposition（ALD） technique,which using molybdenum hexacarbonyl（Mo（CO）6）, oxygen plasma（O2 plasma） as precursors.With the measurement of the thickness of the thin films,we can ascertain the temperature window and the dose time of the precursors of the atomic layer deposition（ALD） self-limiting growth mode.The results showed that: when the deposition temperature are 150,160 and 170℃,the growth of the films are truly linear. So we ascertain that the conditions for atomic layer deposition ALD growth of MoO₃ film: the deposition temperature is 160℃, the dose time of Mo source and oxygen source is 3s, 16 s,respectively and the average growth rate of the film is 0.075 nm/ cycle.（2） A selction of as-deposited MoO₃ films grown at 160℃ were annealed at 300,400,500 and 600℃,respectively,all for 15 minutes in air atmosphere.The results showed that:MoO₃ films annealed in air at 300℃ for 15 minutes can be crystallisation, and a two-phase mixture of α-MoO₃ and β-MoO₃ was observed.When annealed temperature was above 400℃,the β-MoO₃ phase disappeared and the pure orthorhombic α-MoO₃ was observed.And when the annealed temperature reached to 600℃, the films disappeared because of thermal evaporation;（3） The thesis explored the Raman spectra of the MoO₃ films deposited on the Si substrate and the MoO₃ films after H2 exposure in Ar environment. The only major difference on laman spectra of these different substrates are the ratios of the intesities for the peaks at 668,819 and 994cm-1.And when the process of exposing the MoO₃ films to 1% H2 in Ar environment for 2 min,it is observed that a new peak instead appears at a lower wavenumber of 718cm-1, which suggests that the traces of MoO_3-x appear. The X photoelectron spectroscopy shows that atomic ratio of Mo:O is 1:2.49 and the x is equal to 0.51.（4） The above-mentioned MoO_3-x thin films was prepared to a field-effect transistor（FET）,and the I-V characteristics of the field-effect transistor was obtained.The results showed that: when the drain-source voltage Vds was equal to 100 mV, the carrier mobility was caculated from the I-V curves to be 4.311 cm2v-1s-1（μ=4.311 cm2v-1s-1）,and the ON/OFF ratio was less than 100, and the transistor can not be completely switched off.（5）The as-deposited MoO₃ films grown at 160℃ were exposed in Se environment.And the thesis studed the films exposed in Se environment for the analysis of SEM、XRD and Raman spectra,respectively.The results suggested that:when the process temperature reached to 600℃,the MoO₃ film can convert to MoSe2 film. But the MoSe2 films were not continuous, which only analyze the physical properties of the film and can not effectively fabricate the corresponding electronic divices.